THE ELECTRONIC-STRUCTURE OF A MODEL BIMETALLIC CATALYST - SYMMETRY-RESOLVED DENSITY-OF-STATES AT (GAMMA)OVER-BAR FOR CU RU(111)/

The ruthenium hcp(0001) surface covered by a copper monolayer has beco me an important model system for investigating central questions regar ding the catalytic behavior of bimetallic materials. We argue that the dominant modifications of the clean Ru surface electronic structure a re relatively insensitive to the stacking of the layers near the surfa ce, and we therefore carry out surface Green's function TB-LMTO comput ations to determine the symmetry- and layer-resolved density of states at k(\\) = O (($) over bar Gamma) for fee Cu/Ru(111), fee Cu(111) and fee Ru(111). At ($) over bar Gamma there are two irreducible represen tations, a non-degenerate one, ($) over bar Gamma(1), to which the s, p(z), and d(3z-r)(22) states belong and a doubly degenerate one, ($) o ver bar Gamma(2) to which the p(x), p(y); d(xy) d(x-y)(22); and d(xy), d(yx) states belong. While we obtain various new surface resonances an d bound states, our principal finding is that the Cu overlayer suppres ses the upper ($) over bar Gamma(2) subband of Ru at the surface. This finding suggests a simple theoretical interpretation of the X-ray spe ctroscopic observations and a possible basis for understanding the che mical behavior of this material.